ftrace: add nop tracer

A no-op tracer which can serve two purposes:

 1. A template for development of a new tracer.
 2. A convenient way to see ftrace_printk() calls without
    an irrelevant trace making the output messy.

[ mingo@elte.hu: resolved conflicts ]
Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 16e5bb5daaa50b6cb673370c74a65200ed726bc6..d7b2de744631788e61b3fb14dc5600e70bd28d60 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -101,6 +101,16 @@ config SCHED_TRACER
          This tracer tracks the latency of the highest priority task
          to be scheduled in, starting from the point it has woken up.
 
+config NOP_TRACER
+       bool "NOP Tracer"
+       depends on HAVE_FTRACE
+       depends on DEBUG_KERNEL
+       select TRACING
+       help
+         This tracer does nothing. The primary purpose for it is to
+         politely print the output of ftrace_printk() calls without
+         the overhead of an irrelevant trace taking place.
+
 config CONTEXT_SWITCH_TRACER
        bool "Trace process context switches"
        depends on HAVE_FTRACE

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 58ec61c44bd67b28720022dd94c80da7daad966d..73ba13f5a461b02fc54df5a0efbda11f490adc4d 100644 (file)
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_FTRACE) += trace_functions.o
 obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
 obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
+obj-$(CONFIG_NOP_TRACER) += trace_nop.o
 obj-$(CONFIG_STACK_TRACER) += trace_stack.o
 obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
 

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 42f65d0097f09a31f364424aa40e9f0d1e9d253e..447d4b9b6391f135488fe9133c96c97fc6690da2 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -339,6 +339,10 @@ extern int trace_selftest_startup_preemptirqsoff(struct tracer *trace,
 extern int trace_selftest_startup_wakeup(struct tracer *trace,
                                         struct trace_array *tr);
 #endif
+#ifdef CONFIG_NOP_TRACER
+extern int trace_selftest_startup_nop(struct tracer *trace,
+                                        struct trace_array *tr);
+#endif
 #ifdef CONFIG_CONTEXT_SWITCH_TRACER
 extern int trace_selftest_startup_sched_switch(struct tracer *trace,
                                               struct trace_array *tr);

diff --git a/kernel/trace/trace_nop.c b/kernel/trace/trace_nop.c
new file mode 100644 (file)
index 0000000..dafaefb
--- /dev/null
+++ b/kernel/trace/trace_nop.c
@@ -0,0 +1,65 @@
+/*
+ * nop tracer
+ *
+ * Copyright (C) 2008 Steven Noonan <steven@uplinklabs.net>
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/debugfs.h>
+#include <linux/ftrace.h>
+
+#include "trace.h"
+
+static struct trace_array      *ctx_trace;
+
+static void start_nop_trace(struct trace_array *tr)
+{
+       /* Nothing to do! */
+}
+
+static void stop_nop_trace(struct trace_array *tr)
+{
+       /* Nothing to do! */
+}
+
+static void nop_trace_init(struct trace_array *tr)
+{
+       ctx_trace = tr;
+
+       if (tr->ctrl)
+               start_nop_trace(tr);
+}
+
+static void nop_trace_reset(struct trace_array *tr)
+{
+       if (tr->ctrl)
+               stop_nop_trace(tr);
+}
+
+static void nop_trace_ctrl_update(struct trace_array *tr)
+{
+       /* When starting a new trace, reset the buffers */
+       if (tr->ctrl)
+               start_nop_trace(tr);
+       else
+               stop_nop_trace(tr);
+}
+
+static struct tracer nop_trace __read_mostly =
+{
+       .name           = "nop",
+       .init           = nop_trace_init,
+       .reset          = nop_trace_reset,
+       .ctrl_update    = nop_trace_ctrl_update,
+#ifdef CONFIG_FTRACE_SELFTEST
+       .selftest       = trace_selftest_startup_nop,
+#endif
+};
+
+__init static int init_nop_trace(void)
+{
+       return register_tracer(&nop_trace);
+}
+device_initcall(init_nop_trace);

diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index 630715bbd572a6c4da9a711445511b216d6117c7..82db9103b9bc10f726a5d80b2af614fffa281dbd 100644 (file)
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -418,6 +418,15 @@ trace_selftest_startup_preemptirqsoff(struct tracer *trace, struct trace_array *
 }
 #endif /* CONFIG_IRQSOFF_TRACER && CONFIG_PREEMPT_TRACER */
 
+#ifdef CONFIG_NOP_TRACER
+int
+trace_selftest_startup_nop(struct tracer *trace, struct trace_array *tr)
+{
+       /* What could possibly go wrong? */
+       return 0;
+}
+#endif
+
 #ifdef CONFIG_SCHED_TRACER
 static int trace_wakeup_test_thread(void *data)
 {